The development of neural connections in the lobster Homarus americanus will be studied. Intracellular recording from embryonic abdominal muscles has demonstrated that neuromuscular synapses are active as early as the third month of a nine month development. Parallel ultrastructural studies have lead to the same conclusion. These results will be extended using electrophysiological, pharmacological and ultrastructural techniques. In particular, we will attempt to determine: 1) the pattern of innervation of the abdominal muscles in adult and post-larval animals; 2) the time course of growth of the abdominal ganglia, and the roots (nerve tracts) which serve the abdominal musculature; 3) the time course of innervation for the various axons to each of the abdominal muscles; 4) the events involved in formation and maturation of nerve-muscle connections; 5) the properties of the early muscle cell, including the similarities and differences between fast and slow muscle anlagen in regard to resting membrane potential, active membrane properties, ultra structure, presence and location of receptors for the two transmitter substances, and finally, the differences in properties of the synapses on the two types of muscle fibers.